Method for re-ranking documents retrieved from a document database

ABSTRACT

A computer-implemented method for processing documents in a document database includes generating an initial ranking of retrieved documents using an information retrieval system and based upon a user search query, and processing vocabulary words based upon occurrences thereof in at least some of the retrieved documents. Respective relevancies of the vocabulary words based on the occurrences thereof and the user search query are generated. A re-ranking of the retrieved documents is generated based on the relevancies of the vocabulary words.

FIELD OF THE INVENTION

The present invention relates to the field of information retrieval, and more particularly, to a method of information retrieval that enhances identification of relevant documents retrieved from a document database.

BACKGROUND OF THE INVENTION

Information retrieval systems and associated methods search and retrieve information in response to user search queries. As a result of any given search, vast amounts of data may be retrieved. These data may include structured and unstructured data, free text, tagged data, metadata, audio imagery, and motion imagery (video), for example. To compound the problem, information retrieval systems are searching larger volumes of information every year. A study conducted by the University of California at Berkley concluded that the production of new information has nearly doubled between 1999 and 2002.

When an information retrieval system performs a search in response to a user search query, the user may be overwhelmed with the results. For example, a typical search provides the user with hundreds and even thousands of items. The retrieved information includes both relevant and irrelevant information. The user now has the burden of determining the relevant information from the irrelevant information.

One approach to this problem is to build a taxonomy. A taxonomy is an orderly classification scheme of dividing a broad topic into a number of predefined categories, with the categories being divided into sub-categories. This allows a user to navigate through the available data to find relevant information while at the same time limiting the documents to be searched. However, creating a taxonomy and identifying the documents with the correct classification is very time consuming. Moreover, a taxonomy requires continued maintenance to categorize new information as it becomes available.

Another approach is to use an information retrieval system that groups the results to assist the user. For example, the Vivisimo Clustering Engine™ automatically organizes search results into meaningful hierarchical folders on-the-fly. As the information is retrieved, it is clustered into categories that are intelligently selected from the words and phrases contained in the search results themselves. This results in the categories being up-to-date and fresh as the contents therein.

Visual navigational search approaches are provided in U.S. Pat. Nos. 6,574,632 and 6,701,318 to Fox et al., the contents of which are hereby incorporated herein by reference. Fox et al. discloses an information retrieval and visualization system utilizing multiple search engines for retrieving documents from a document database based upon user input queries. Each search engine produces a common mathematical representation of each retrieved document. The retrieved documents are then combined and ranked. A mathematical representation for each respective document is mapped onto a display. Information displayed includes a three-dimensional display of keywords from the user input query. The three-dimensional visualization capability based upon the mathematical representation of information within the information retrieval and visualization system provides users with an intuitive understanding, with relevance feedback/query refinement techniques that can be better utilized, resulting in higher retrieval accuracy.

Despite the continuing development of search engines and result visualization techniques, there is still a need to quickly and efficiently search large document collections and present the results in a meaningful manner to the user.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of the present invention to assist a user in identifying relevant documents and discarding irrelevant documents after the documents have been retrieved using an information retrieval system.

This and other objects, features, and advantages in accordance with the present invention are provided by a computer-implemented method for processing documents in a document database comprising generating an initial ranking of retrieved documents using an information retrieval system and based upon a user search query, generating a plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents, and generating respective relevancies of the vocabulary words based on the occurrences thereof and the user search query. A re-ranking of the retrieved documents based on the relevancies of the vocabulary words is generated. The computer-implemented method in accordance with the present invention advantageously allows a user to identify relevant documents and discard irrelevant documents after the documents have been retrieved using the information retrieval system.

The computer-implemented method may further comprise generating the plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents before the processing. In this embodiment, the vocabulary words are provided by the words in the retrieved documents.

Alternatively, a user may select a vocabulary comprising the plurality of vocabulary words before the processing, with the vocabulary words corresponding to the user search topic. In this embodiment, the vocabulary words may be based upon words in at least one predetermined document, and the predetermined document does not need to be part of the retrieved documents. In addition, vocabulary words may be added to the vocabulary based upon occurrences of words in at least some of the retrieved documents. A quality of the vocabulary may be determined based upon how many vocabulary words are added thereto.

The computer-implemented method may further comprise selecting N top ranked documents from the retrieved documents before processing the plurality of vocabulary words, with N being an integer greater than 1. Generating the respective relevancies and generating the re-ranking are with respect to the N top-ranked documents.

Generating the respective relevancies of the vocabulary words may comprise counting how many times a respective vocabulary word is used in the N top ranked documents, and counting how many of the N top ranked documents uses the respective vocabulary word. A word/document ratio for each respective vocabulary word may be generated based upon the counting, and if the word/document ratio is less than a threshold, then the relevancy of the word is not used when generating the re-ranking of the N top ranked documents.

The computer-implemented method may further comprise determining which documents from at least some of the retrieved documents are relevant to the user search query, and generating the re-ranking of the retrieved documents may also be based on the relevant documents. A determination may be made if the respective vocabulary words are relevant to the user search query, and then a determination may be made as to whether the documents are relevant based upon the relevant vocabulary words.

The computer-implemented method may further comprise determining a respective source of at least some of the retrieved documents, and assigning priority to documents provided by preferred sources. Generating the re-ranking of the retrieved documents may also be based on documents with preferred sources. A second re-ranking of the retrieved documents based upon a combination of the initial ranking and the re-ranking of the retrieved documents may be generated. The re-ranked documents may also be displayed.

Another aspect of the present invention is directed to a computer-readable medium having stored thereon a data structure for processing documents in a document database as defined above. Yet another aspect of the present invention is directed to a computer implemented system for processing documents in a document database as also defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for processing documents in a document database in accordance with the present invention.

FIG. 2 is an initial query display screen in accordance with the present invention.

FIGS. 3 a and 3 b respectively illustrate in accordance with the present invention a display screen for starting a new vocabulary and for using an existing vocabulary.

FIG. 4 is a display screen illustrating the query results using the “piracy” vocabulary in accordance with the present invention.

FIGS. 5 and 6 are display screens illustrating the word lists from a selected document in accordance with the present invention.

FIG. 7 is a display screen illustrating another version of a word list from a selected document in accordance with the present invention.

FIGS. 8-11 are display screens illustrating the document rankings for different ranking parameters in accordance with the present invention.

FIG. 12 is bar graph illustrating the number of relevant documents in the retrieved documents provided by different ranking parameters in accordance with the present invention.

FIG. 13 is a block diagram of a computer-based system for processing documents in a document database in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.

Referring initially to FIG. 1, the present invention is directed to a computer-implemented method for processing documents in a document database. From the start (Block 20), the method comprises generating an initial ranking of retrieved documents using an information retrieval system and based upon a user search query at Block 22. A plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents is generated at Block 24, and respective relevancies of the vocabulary words based on the occurrences thereof and the user search query is generated at Block 26. A re-ranking of the retrieved documents based on the relevancies of the vocabulary words is generated at Block 28. The method further comprises displaying the retrieved documents after having been re-ranked at Block 30. The method ends at Block 32.

The computer-implemented method for processing documents in a document database advantageously allows a user to identify relevant documents and discard irrelevant documents after the documents have been retrieved using an information retrieval system. The user may be a human user or a computer-implemented user. When the user is computer-implemented, identifying relevant documents and discarding irrelevant documents is autonomous. The information retrieval system includes an input interface for receiving the user search query, and a search engine for selectively retrieving documents from a document database.

The search engine is not limited to any particular search engine. An example search engine is the Advanced Information Retrieval Engine (AIRE) developed at the Information Retrieval Laboratory of the Illinois Institute of Technology (IIT). AIRE is a portable information retrieval engine written in Java, and provides a foundation for exploring new information retrieval techniques. AIRE is regularly used in the Text Retrieval Conference (TREC) held each year, which is a workshop series that encourages research in information retrieval from large text applications by providing a large text collection, uniform scoring procedures, and a forum for organizations interested in comparing their results.

Since TREC uses a dataset with known results, this facilities evaluation of the present invention. An example search topic from TREC is “piracy,” which is used for illustrating and evaluating the present invention. AIRE provides the initial ranking of the retrieved documents based upon the “piracy” user search query. The number and/or order of the relevant documents in the initial ranking is the baseline or reference that will be compared to the number of relevant documents in the re-ranked documents.

As will be discussed in further detail below, there are a variety of word and document relevancy options available to the user. Individually or in combination, these options improve the retrieval accuracy of a user search query. Implementation of the present invention is in the form of an algorithm requiring user input, and this input is provided via the graphical user interface (GUI) associated with AIRE.

The initial AIRE query screen for assisting a user for providing the relevant feedback for re-ranking the retrieved documents is provided in FIG. 2. The “piracy” user search query is provided in section 40, and the user has the option in section 42 of starting a new vocabulary or using an existing vocabulary. In this case, a new vocabulary is being started.

A description of the topic of interest is provided in section 44, which is directed to “what modern instances have there been of good old-fashioned piracy, the boarding or taking control of boats?” A narrative providing more detailed information about the description is provided in section 46. The narrative in this case states that “documents discussing piracy on any body of water are relevant, documents discussing the legal taking of ships or their contents by a national authority are non-relevant, and clashes between fishing boats over fishing are not relevant unless one vessel is boarded.” The words in the description and narrative sections 44, 46 were not included as part of the user search query. Nonetheless, the user has the option of making the words in the description and narrative sections 44, 46 part of the user search query by selecting these sections along with section 40.

When the user selects starting a new vocabulary in section 42, a new vocabulary screen appears as illustrated in FIG. 3 a. Here the user enters a name for the new vocabulary in section 50, which in the illustrated example is “piracy.” In this case, the title of the new vocabulary is also the user search query. Alternatively, if the user had selected using an existing vocabulary in section 42, then the existing vocabulary screen appears as illustrated in FIG. 3 b. A topic of interest may overlap two different vocabularies so selecting a preferred vocabulary would be helpful. As in the illustrated example, piracy relates to maritime instead of the illegal coping of movies and songs. Consequently, an existing vocabulary, such as “maritime” may be selected in section 52, which already includes relevant words that would be found in the retrieved documents. In fact, the vocabulary words in the existing vocabularies may be taken from the words in preferred documents that are known to be relevant to the user search query. The preferred document may or may not be part of the retrieved documents.

The initial ranking of the retrieved documents is a very large number with respect to “piracy,” which includes both relevant and irrelevant documents. Before generating a new vocabulary, the user selects the N top ranked documents in section 48 in FIG. 2. In the illustrated example, the number of top ranked documents to be re-ranked is 100.

To build a new vocabulary, an algorithm counts the number of times words are used throughout the top 100 retrieved documents. The words may be counted at their stemmed version, although this is not absolutely necessary. A domain vocabulary can also be built by providing a list of relevant documents. The information collected for each word in each document is the number of times the word was used in the document, and the number of documents in the top 100 top ranked documents that used the word.

Next, document statistics are calculated for determining how useful each word is to the N top ranked documents. Useless words are not used to calculate information about the document. Useless words are words that do not provide meaning, such as stop words (e.g., am, are, we) or words that act as stop words within the domain (e.g., computer in computer science literature). Statistics used for determining a useless word may include, but are not limited to, the following:

a) word/document ratio=1 (the word needs to appear more than once in a document to be useful);

b) word/document ratio>20 (this determines a meaningful threshold; and a range of thresholds may be used instead of a single threshold); and

c) the number of documents=1 (the word needs to appear in more than one document).

Based upon the criteria in a) through c), the vocabulary thus comprises for each useful word the number of times it was used (traditional term frequency only within a single document, the number of documents using the word (traditional document frequency), and the word/document ratio.

After a list of vocabulary words provided by the top 100 ranked documents and the user search query (i.e., “piracy”) has been compiled, the relevancy of the vocabulary words are set. Some vocabulary words may be more relevant/irrelevant than other words. Word relevance is set by topic, which in this case is “piracy” as related to “maritime.” Relevant words are useful words that describe the topic “piracy.” Irrelevant words are words that do not describe the topic, and are an indicator of irrelevant documents.

Relevance is set to a value of 1 for the query terms supplied by the user. The relevance value of a vocabulary word is based upon the number of times the word was relevant and on the number of times the word was irrelevant. The relevancy value of a word can be written as follows: Relevancy Value=(#Rel−#Irrel)/(#Rel+#Irrel). A word can be deemed relevant, for example, if the relevancy value>0.5, and irrelevant if the relevancy value<−0.5. The 0.5 and −0.5 are example values and may be set to other values as readily appreciated by those skilled in the art. In addition, a range of thresholds may be used instead of a single threshold.

To calculate document statistics, information is calculated based on the words in the N top ranked documents. A document comprises a set of words, and a word can appear 1 or more times therein. Each document is essentially unstructured text, and a word can be characterized as new, useless or useful. A new word is new to the vocabulary. In a training session, i.e., starting with a new vocabulary, all the words are in the vocabulary. A useless word is not used in document calculations, and as noted above, these words do not provide meaning. Useless words are stop words, such as am, are, we, or words that act as stop words within the domain, such as computer in computer science literature. A useful word is a word that will be used in the document statistics.

A useful word can be further classified as relevant, irrelevant or neutral. As defined by these classification terms, a relevant word is important to the topic, and an irrelevant word is not useful to the topic and is usually an indicator of a bad document. A neutral word is one in which the status of the word as related to the topic has not been determined.

To calculate the re-ranking of the retrieved documents, an algorithmic approach is used to rate the documents. The algorithmic approach uses the relevancy information discussed above. The output of the initial document ranking by AIRE is a list of the documents rated from 1 to 100, where 100 was selected by the user. The lowest number indicates the best ranking. Alternatively, the highest number could be the best ranking.

Three different relevancy values are used to re-rank the documents. The first relevancy value is based upon following expression: Unique Rel−Unique Irrel→UniqueRel   (1) The number of unique relevant words in the document is counted, and the number of irrelevant words in the document is counted. The sum of the irrelevant words is subtracted from the sum of the relevant words. As an observation, this calculation becomes more useful when there are only individual words identified. That is, entire documents have not been identified as relevant/irrelevant.

The second relevancy value is based upon following expression: Rel NO Freq−Irrel NO Freq→RelNOFreq   (2) Here the importance of unique relevant/irrelevant words in the document is determined. The sum of the number of times the word is irrelevant in the vocabulary is subtracted from the sum of the number of times the word is relevant in the vocabulary. A word that appears more often in the vocabulary will have a higher weight than words that just appeared a couple of times. As an observation, this value is tightly coupled with the Unique Rel−Irrel value in expression (1), particularly when all the values are positive.

The third relevancy value is based upon following expression: Rel Freq−Ir Freq→RelFreq   (3) Here the importance of unique relevant/irrelevant words and their frequency in the documents is determined. The sum of the number of times the word is relevant in the vocabulary is multiplied by the number of times the word is used in the document. The sum of the number of times the word is irrelevant in the vocabulary is multiplied by the number of times the word is used in the document. The irrelevancy frequency sum is subtracted from the relevancy frequency sum. A word that appears more often in the vocabulary will have a higher weight than words that just appeared a couple of times. As an observation, this value is more useful when relevant/irrelevant document examples have been trained in the system.

To identify bad documents there are two techniques. One is based upon the over usage of specific words, and the other is based on a low UniqueRel value as defined in expression (1). With respect to over usage of specific words, documents that have a word appearing more than 100 times, for example, in a document are identified as bad documents. Also, words that are used very frequently in a few documents are determined to have a usefulness set to 0. The user has the option of setting the number of times the word appearing in a document is to be considered as a bad value.

The initial ranking of the N top ranked retrieved documents is re-ranked from the highest relevancy values to the lowest relevancy values for expressions 1) UniqueRel, 2) RelNOFreq and 3) RelFreq. The re-ranking of each document is averaged for the three expressions to obtain the final re-ranking of the retrieved documents. In each of the respective document rankings, bad documents are sent to the bottom of the document list. Two different techniques may be used in moving the bad documents to the bottom. One technique is jumping number ordering—which assigns large values to the document's ranking so that it remains at the bottom. The other technique is smooth number ordering—which assigns continuous ranking numbers to the documents.

With respect to the UniqueRel numbers obtained for the documents, all documents with the smallest UniqueRel number are identified as bad. If the second smallest UniqueRel numbers are under 30%, for example, then these documents are also characterized as bad. Additional small UniqueRel documents can be added until the total number of documents does not exceed 30%. In other words, taking the percentage of the lowest number of UniqueRel from the percentage of the highest number of UniqueRel should not exceed 30%. The user has the option of setting this threshold to a value other than 30%, as readily appreciated by those skilled in the art.

In re-ranking the N top ranked retrieved documents, it is also possible to assign priority to a document based upon the source of the document. For example, National Scientific would carry a greater weight than The National Enquirer.

Management of the data will now be discussed with reference to the user display screens provided in FIGS. 4-7. The data are handled at two levels: vocabulary and topic. The vocabulary is used to define the domain, and includes for each word the number of times used in each document and the number of documents the word appeared. A vocabulary can be used by multiple topics, such as in the form of a predefined vocabulary. However, it is preferable to avoid using the same document to train multiple times. With respect to the managing the data by topic, the relevance/irrelevance of the words and documents are used, as well as using the query search terms.

The majority of the data management deals with the user interface. The user has the ability to view any document and the word information associated therewith. The user has the ability to identify relevant/irrelevant documents and words to use for training, i.e., building the vocabulary. The user has the ability to identify words for a future AIRE query. The user has the ability to run a new AIRE query or re-run the ranking algorithm in accordance with the present invention on the current data based on information supplied to the system.

The initial ranking of the retrieved documents using the “piracy” vocabulary is illustrated in FIG. 4. Column 60 lists the titles of the documents in order from high to low. The AIRE relevancy is provided in column 62. After the retrieved documents have been re-ranked while taking into account the “piracy” vocabulary, this re-ranking is averaged with the initial ranking provided by AIRE in column 62. The combination of the two rankings is provided in column 64. For example, the highest ranked document in column 62 is now the sixth ranked document in column 64.

Selecting any one of the listed titles in column 60 will display the document words. The relevancy of each vocabulary word with respect to each document is provided in column 66. For each document, the document may be marked as relevant (column 68), mildly relevant (column 70) or off topic (column 72). In addition, the total word count for each document is provided in column 74, and comments associated with any of the documents may be added or viewed by selecting the icon in column 76.

If the user desires to view the entire document, then the user highlights the icon in column 78 next to the title of interest. The information for each document is stored in a respective file, as indicated by column 80. To further assist the user, when a document is marked as relevant, then the row associated with the relevant document is highlighted.

By selecting on the title of a particular document in column 60, the words in that document are displayed in column 81 in an order based upon how many times they are used in the document (FIG. 5). This screen also shows how the words are set in terms of relevancy. The number of times each vocabulary word is used in the document is listed in column 82, and the number of documents that uses the word is listed in column 84. The word/document ratio is provided in column 86. The vocabulary words initially marked by the user as relevant are indicated by the numeral 1 in columns 88 and 92. If the vocabulary word is irrelevant, then the numeral −1 is placed instead in column 90.

The highlighted section in FIG. 5 also indicates the relevant words. However, the words “copyright” and “software” are not related to the topic “piracy.” While still in this screen, the user can sort the words by relevancy and usage by selecting the appropriate characterization: R for relevant (column 100), I for irrelevant (column 102), N for neutral (column 104) and U for useless (column 106). If the word is already marked as relevant, then no action is required for that word.

The screen display illustrated in FIG. 6 illustrates the selection of certain vocabulary words via column 102 as irrelevant. An alternative to the display screen in FIGS. 5 and 6 when viewing the words in a particular document is provided in FIG. 7. In this particular screen, the user also has the option of selecting in section 110′ whether the document is relevant, mildly relevant or off topic. The user also has the option of adding new words via section 112′ to the vocabulary.

The user also has the option of selecting multiple views (as labeled) according to user preference. For instance, tab 120 list all the vocabulary words in a document, tab 122 list the vocabulary words in alphabetical order, tab 124 list the vocabulary words marked as relevant, tab 126 list the vocabulary words marked as irrelevant, tab 128 list the vocabulary words marked as new, and statistics of the vocabulary words may be obtained by selecting tab 130. In FIG. 7, the user has the option of selecting tabs with respect to the relevant/irrelevant/neutral words in the documents. Tab 140′ list the relevant words in the documents, tab 142′ lists the irrelevant words in the documents, tab 144′ list the neutral words in the documents, and tab 146′ list the useless words in the documents.

Comparing various document ranking results of the computer-implemented method for processing documents in a document database in accordance with the present invention will now be compared to the baseline results provided by AIRE, that is, the initial ranking of the retrieved documents. The display screens provided in FIGS. 4 and 8-11 will now be referenced. The initial ranking from 1 to 20 (column 62) of the retrieved documents is provided in column 60 as shown in FIG. 4. The document titles corresponding to the “piracy” vocabulary rankings from 1 to 20 (column 66) are listed in column 60 in FIG. 8. A visual comparison can be made between the relationships in the ranked baseline documents versus the ranked documents provided by the most relevant “piracy” vocabulary words.

Combining the AIRE ranking and the “piracy” vocabulary ranking to obtain a new ranking from 1 to 20 (column 64) is provided in column 60 in FIG. 9. In lieu of creating a new vocabulary as discussed above, an existing vocabulary may be used. For example, the results of a predefined “maritime” vocabulary have now been combined with the AIRE results. The documents ranked from 1 to 20 (column 64) corresponding to this re-ranking are listed in column 60 in FIG. 10. As yet another comparison, the document titles corresponding to only the “maritime” vocabulary rankings from 1 to 20 (column 66) are listed in column 60 in FIG. 11. A visual comparison can again be made between the relationships in the ranked baseline documents provided by AIRE in FIG. 4 versus the ranked documents provided by the most relevant “maritime” vocabulary words in FIG. 11.

The results of the various approaches just discussed for re-ranking the retrieved documents will now be discussed with reference to FIG. 12. This discussion is based upon the number of relevant documents in the top 5, 10, 15, 20 and 30 ranked or re-ranked documents. The first set of bar graphs correspond to the baseline AIRE rankings provided in columns 60 and 62 in FIG. 4. In the 5 top ranked documents there was 1 relevant document; in the 10 top ranked documents there were 2 relevant documents; in the 15 top ranked documents there were 4 relevant documents; in the 20 top ranked documents there were 5 relevant documents, and in the 30 top ranked documents there were 6 relevant documents.

When the AIRE ranking was combined with the “piracy” vocabulary ranking as provided in columns 60, 64 in FIG. 9 there was a decrease in the number of relevant documents in the re-ranked documents, as illustrated by the second set of bar graphs. In contrast, the number of relevant documents increases when the AIRE ranking and the “piracy” vocabulary ranking using the identification of irrelevant words are combined, as illustrated by the third set of bar graphs.

The fourth set of bar graphs is based upon a combined ranking of the AIRE ranking and the “maritime” vocabulary ranking as provided in columns 60, 64 in FIG. 10. Here, there is a greater increase in the number of relevant documents in the re-ranked documents.

A further increase in the number of relevant documents in the re-ranked documents is based upon just the “maritime” vocabulary as provided in columns 60, 66 in FIG. 11. In the 5 top ranked documents there were 5 relevant documents; in the 10 top ranked documents there were 10 relevant documents; in the 15 and 20 top ranked documents there were 12 relevant documents for each; and in the 30 top ranked documents there were 13 relevant documents.

As best illustrated in FIG. 12, the present invention advantageously allows the user to re-rank the retrieved documents from a document database so that more of the top ranked documents are relevant documents. A vocabulary is built based upon the user search query, or an existing vocabulary is selected. A newly created vocabulary is analyzed to identify the importance of specific words and to also identify problem words. Relevant/irrelevant words are identified through the user search query, applicable algorithms and via user input. In addition, based upon the relevancy of the words, relevant/irrelevant documents are identified. The irrelevant documents are moved to the bottom of the ranking.

The method may be implemented in a computer-based system 150 for processing documents in a document database, as illustrated in FIG. 13. The computer-based system 150 comprises a plurality of first through fourth modules 152-158. The first module 152 generates an initial ranking of retrieved documents using an information retrieval system and based upon a user search query. The second module 154 generating a plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents. The third module 156 generates respective relevancies of the vocabulary words based on the occurrences thereof and the user search query. The fourth module 158 generates a re-ranking of the retrieved documents based on the relevancies of the vocabulary words. A display 160 is connected to the computer-based system 150 for displaying the re-ranked documents.

Another aspect of the present invention is directed to a computer-readable medium having stored thereon a data structure for processing documents in a document database as defined above.

Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims. 

1. A computer-implemented method for processing documents in a document database comprising: generating an initial ranking of retrieved documents using an information retrieval system and based upon a user search query; processing a plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents; generating respective relevancies of the vocabulary words based on the occurrences thereof and the user search query; and generating a re-ranking of the retrieved documents based on the relevancies of the vocabulary words.
 2. A computer-implemented method according to claim 1 further comprising generating the plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents before the processing.
 3. A computer-implemented method according to claim 1 further comprising selecting a vocabulary comprising the plurality of vocabulary words before the processing.
 4. A computer-implemented method according to claim 3 wherein the plurality of vocabulary words are based upon words in at least one predetermined document.
 5. A computer-implemented method according to claim 4 wherein the at least one predetermined document is not part of the retrieved documents.
 6. A computer-implemented method according to claim 3 further comprising adding vocabulary words to the vocabulary based upon occurrences of words in at least some of the retrieved documents.
 7. A computer-implemented method according to claim 6 further comprising determining a quality of the vocabulary based upon how many vocabulary words are added thereto.
 8. A computer-implemented method according to claim 1 further comprising selecting N top ranked documents from the retrieved documents before processing the plurality of vocabulary words, with N being an integer greater than 1; and wherein generating the respective relevancies and generating the re-ranking are with respect to the N top-ranked documents.
 9. A computer-implemented method according to claim 8 wherein generating the respective relevancies of the vocabulary words comprises: counting how many times a respective vocabulary word is used in the N top ranked documents; and counting how many of the N top ranked documents uses the respective vocabulary word.
 10. A computer-implemented method according to claim 9 further comprising generating a word/document ratio for each respective vocabulary word based upon the counting, and if the word/document ratio is less than a threshold, then the relevancy of the word is not used when generating the re-ranking of the N top ranked documents.
 11. A computer-implemented method according to claim 1 further comprising determining which documents from at least some of the retrieved documents are irrelevant to the user search query; and wherein generating the re-ranking of the retrieved documents is also based on the irrelevant documents.
 12. A computer-implemented method according to claim 1 further comprising determining which documents from at least some of the retrieved documents are relevant to the user search query; and wherein generating the re-ranking of the retrieved documents is also based on the relevant documents.
 13. A computer-implemented method according to claim 12 further comprising determining if the respective vocabulary words are relevant to the user search query; and wherein determining the relevant documents is based upon the relevant vocabulary words.
 14. A computer-implemented method according to claim 1 further comprising determining a respective source of at least some of the retrieved documents, and assigning priority to documents provided by preferred sources; and wherein generating the re-ranking of the retrieved documents is also based on documents with preferred sources.
 15. A computer-implemented method according to claim 1 further comprising generating a second re-ranking of the retrieved documents based upon a combination of the initial ranking and the re-ranking of the retrieved documents.
 16. A computer-implemented method according to claim 1 further comprising displaying the re-ranked documents.
 17. A computer-implemented method for processing documents in a document database, the documents having an initial ranking based upon a user search query, the method comprising; selecting N top ranked documents from the retrieved documents, with N being an integer greater than 1; processing a plurality of vocabulary words based upon occurrences thereof in the N top ranked documents; generating respective relevancies of the vocabulary words based on the occurrences thereof in the N top ranked documents and the user search query; generating a re-ranking of the N top ranked documents based on the relevancies of the vocabulary words; and displaying the re-ranked documents.
 18. A computer-implemented method according to claim 17 further comprising generating the plurality of vocabulary words based upon occurrences thereof in the N top ranked documents.
 19. A computer-implemented method according to claim 17 further comprising selecting a vocabulary comprising the plurality of vocabulary words before the processing.
 20. A computer-implemented method according to claim 19 wherein the plurality of vocabulary words are based upon words in at least one predetermined document.
 21. A computer-implemented method according to claim 20 wherein the at least one predetermined document is not part of the retrieved documents.
 22. A computer-implemented method according to claim 20 further comprising adding vocabulary words to the vocabulary based upon occurrences of words in at least some of the retrieved documents.
 23. A computer-implemented method according to claim 22 further comprising determining a quality of the vocabulary based upon how many vocabulary words are added thereto.
 24. A computer-implemented method according to claim 17 wherein generating the respective relevancies of the vocabulary words comprises: counting how many times a respective vocabulary word is used in the N top ranked documents; and counting how many of the N top ranked documents uses the respective vocabulary word.
 25. A computer-implemented method according to claim 24 further comprising generating a word/document ratio for each respective vocabulary word based upon the counting, and if the word/document ratio is less than a threshold, then the relevancy of the word is not used when generating the re-ranking of the N top ranked documents.
 26. A computer-implemented method according to claim 17 further comprising determining which documents from at least some of the retrieved documents are irrelevant to the user search query; and wherein generating the re-ranking of the retrieved documents is also based on the irrelevant documents.
 27. A computer-implemented method according to claim 17 further comprising determining which documents from the N top ranked documents are relevant to the user search query; and wherein generating the re-ranking of the retrieved documents is also based on the relevant documents.
 28. A computer-implemented method according to claim 27 further comprising determining if the respective vocabulary words are relevant to the user search query; and wherein determining the relevant documents is based upon the relevant vocabulary words.
 29. A computer-implemented method according to claim 17 further comprising determining a respective source of the N top ranked documents, and assigning priority to documents provided by preferred sources; and wherein generating the re-ranking of the N top ranked documents is also based on documents with preferred sources.
 30. A computer-implemented method according to claim 17 further comprising generating a second re-ranking of the N top ranked documents based upon a combination of the initial ranking and the re-ranking of the N top ranked documents.
 31. A computer-readable medium having stored thereon a data structure for processing documents in a document database, the computer-readable medium comprising: a first data field for generating an initial ranking of retrieved documents using an information retrieval system and based upon a user search query; a second data field for processing a plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents; a third data field for generating respective relevancies of the vocabulary words based on the occurrences thereof and the user search query; and a fourth data field for generating a re-ranking of the retrieved documents based on the relevancies of the vocabulary words.
 32. A computer-readable medium according to claim 31 further comprising a fifth data field for generating the plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents before the processing.
 33. A computer-readable medium according to claim 31 further comprising a sixth data field for selecting a vocabulary comprising the plurality of vocabulary words before the processing, the plurality of vocabulary words corresponding to the user search topic.
 34. A computer-readable medium according to claim 33 wherein the plurality of vocabulary words are based upon words in at least one predetermined document.
 35. A computer-readable medium according to claim 34 wherein the at least one predetermined document is not part of the retrieved documents.
 36. A computer-readable medium according to claim 34 further comprising a seventh data field for adding vocabulary words to the vocabulary based upon occurrences of words in at least some of the retrieved documents.
 37. A computer-readable medium according to claim 36 further comprising an eighth data field for determining a quality of the vocabulary based upon how many vocabulary words are added thereto.
 38. A computer-readable medium according to claim 31 further comprising a ninth data field for selecting N top ranked documents from the retrieved documents before processing the plurality of vocabulary words, with N being an integer greater than 1; and wherein generating the respective relevancies in said third data field and generating the re-ranking in said fourth data field are with respect to the N top-ranked documents.
 39. A computer-readable medium according to claim 38 wherein generating the respective relevancies of the vocabulary words comprises: a tenth data field for counting how many times a respective vocabulary word is used in the N top ranked documents; and an eleventh data field for counting how many of the N top ranked documents uses the respective vocabulary word.
 40. A computer-readable medium according to claim 39 further comprising a twelfth data field for generating a word/document ratio for each respective vocabulary word based upon the counting, and if the word/document ratio is less than a threshold, then the relevancy of the word is not used when generating the re-ranking of the N top ranked documents.
 41. A computer-readable medium according to claim 31 further comprising a thirteenth data field for determining which documents from at least some of the retrieved documents are relevant to the user search query; and wherein generating the re-ranking of the retrieved documents in said fourth data field is also based on the relevant documents.
 42. A computer-readable medium according to claim 41 further comprising a fourteenth data field for determining if the respective vocabulary words are relevant to the user search query; and wherein determining the relevant documents in said third data field is based upon the relevant vocabulary words.
 43. A computer-readable medium according to claim 31 further comprising a fifteenth data field for determining a respective source of at least some of the retrieved documents, and assigning priority to documents provided by preferred sources; and wherein generating the re-ranking of the retrieved documents in said fourth data field is also based on documents with preferred sources.
 44. A computer-readable medium according to claim 31 further comprising a sixteenth data field for generating a second re-ranking of the retrieved documents based upon a combination of the initial ranking and the re-ranking of the retrieved documents.
 45. A computer-readable medium according to claim 31 further comprising a seventeenth data field for displaying the re-ranked documents.
 46. A computer implemented system for processing documents in a document database comprising: a first module for generating an initial ranking of retrieved documents using an information retrieval system and based upon a user search query; a second module for processing a plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents; a third module for generating respective relevancies of the vocabulary words based on the occurrences thereof and the user search query; and a fourth module for generating a re-ranking of the retrieved documents based on the relevancies of the vocabulary words.
 47. A computer implemented system according to claim 46 further comprising a fifth module for generating the plurality of vocabulary words based upon occurrences thereof in at least some of the retrieved documents before the processing.
 48. A computer implemented system according to claim 46 further comprising a sixth module for selecting a vocabulary comprising the plurality of vocabulary words before the processing.
 49. A computer implemented system according to claim 48 wherein the plurality of vocabulary words are based upon words in at least one predetermined document.
 50. A computer implemented system according to claim 49 wherein the at least one predetermined document is not part of the retrieved documents.
 51. A computer implemented system according to claim 49 further comprising a seventh module for adding vocabulary words to the vocabulary based upon occurrences of words in at least some of the retrieved documents.
 52. A computer implemented system according to claim 51 further comprising an eighth module for determining a quality of the vocabulary based upon how many vocabulary words are added thereto.
 53. A computer implemented system according to claim 46 further comprising a ninth module for selecting N top ranked documents from the retrieved documents before processing the plurality of vocabulary words, with N being an integer greater than 1; and wherein generating the respective relevancies in said third module and generating the re-ranking in said fourth module are with respect to the N top-ranked documents.
 54. A computer implemented system according to claim 53 wherein generating the respective relevancies of the vocabulary words comprises: a tenth module for counting how many times a respective vocabulary word is used in the N top ranked documents; and an eleventh module for counting how many of the N top ranked documents uses the respective vocabulary word.
 55. A computer implemented system according to claim 54 further comprising a twelfth module for generating a word/document ratio for each respective vocabulary word based upon the counting, and if the word/document ratio is less than a threshold, then the relevancy of the word is not used when generating the re-ranking of the N top ranked documents.
 56. A computer implemented system according to claim 46 further comprising a thirteenth module for determining which documents from at least some of the retrieved documents are irrelevant to the user search query; and wherein generating the re-ranking of the retrieved documents in said fourth module is also based on the irrelevant documents.
 57. A computer implemented system according to claim 46 further comprising a fourteenth module for determining which documents from at least some of the retrieved documents are relevant to the user search query; and wherein generating the re-ranking of the retrieved documents in said fourth module is also based on the relevant documents.
 58. A computer implemented system according to claim 57 further comprising a fifteenth module for determining if the respective vocabulary words are relevant to the user search query; and wherein determining the relevant documents in said third module is based upon the relevant vocabulary words.
 59. A computer implemented system according to claim 46 further comprising a sixteenth module for determining a respective source of at least some of the retrieved documents, and assigning priority to documents provided by preferred sources; and wherein generating the re-ranking of the retrieved documents in said fourth module is also based on documents with preferred sources.
 60. A computer implemented system according to claim 46 further comprising a seventeenth module for generating a second re-ranking of the retrieved documents based upon a combination of the initial ranking and the re-ranking of the retrieved documents.
 61. A computer implemented system according to claim 46 further comprising a display for displaying the re-ranked documents. 